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Models Performance and Robustness for Simulating Drainage and Nitrate-Nitrogen Fluxes without Recalibration

Jay D. Jabro, Ann D. Jabro, Steven L. Fales
Soil Science Society of America journal 2012 v.76 no.6 pp. 1957-1964
Dactylis glomerata, agricultural forecasts, calibration, carbon sinks, computers, corn soils, drainage, environmental impact, experimental design, fertilizer application, fractionation, frozen soils, groundwater, hydrologic models, intensive livestock farming, leaching, lysimeters, model validation, nitrates, nitrogen, nitrogen fertilizers, pastures, silt loam soils, simulation models, snow, snowmelt, soil nutrient dynamics, soil water movement, water transportation
Intensively grazed pastures generate nitrate-nitrogen (NO₃–N) contaminated groundwater creating grave environmental concern. Computer models simulate and forecast appropriate agricultural practices to reduce environmental impact. Model validation is an essential process in evaluation and field application of computer simulation models. The objectives of this study were to assess and compare robustness and performance of three models—LEACHM (Leaching Estimation and Chemistry Model), NCSWAP (Nitrogen and Carbon Cycling in Soil, Water, And Plant), and SOIL-SOILN—for simulating drainage flux and NO₃–N leaching in an intense pasture system without recalibration. A 3-yr study was conducted on a Hagerstown silt loam to measure drainage and NO₃–N fluxes below 1 m depth from N-fertilized orchardgrass (Dactylis glomerata L.) using intact core lysimeters. Five N-fertilizer treatments were replicated five times in a randomized complete block experimental design. The models were validated under orchardgrass using soil, water, and N transformation rate parameters and C pools fractionation derived from a previous study conducted on similar soils under corn (Zea mays L.). The model efficiency (MEF) of drainage and NO₃–N fluxes were 0.53, 0.69 for LEACHM; 0.75, 0.39 for NCSWAP; and 0.94, 0.91 for SOIL-SOILN. The models failed to produce reasonable simulations of drainage and NO₃–N fluxes in January, February, and March due to limited water movement associated with frozen soil and snow accumulation and melt. The differences between simulated and measured NO₃–N leaching and among models’ performances may also be related to soil N and C transformation processes embedded in the models. Generally, the results demonstrate the potential of these three models to reasonably simulate annual and monthly drainage and NO₃–N fluxes under the pasture system without recalibration.